Spark plug



0. C. ROHDE Feb. 23', 1937.

SPARK PLUG Filed April so, 1936 FIE-.2

M y W M Patented Feb. 23, 1937 UNITED STATES PATENT OFFICE pion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application April 30,

4 Claims.

This invention relates to a spark plug and particularly to a plug which may be made of relatively small diameter. 7

The object of the invention is to produce a plug of simple construction which will be economical and eflicient even when the diameter is relatively small.

Details 01 the invention will appear as the description proceeds.

In the accompanying drawing forming a part of this specification Figure 1 is an elevation of one form of spark plug embodying the invention; Fig. 2 is a longitudinal section of the plu shown in Fig. 1 and Fig. 3 is a section similar to Fig. 2 but showing a slightly modified form.

The plug shown in the drawing comprises a shell in having a screw threaded end ll adapted to be screwed'into the usual opening in the cylinder of an internal combustion motor or the like. Attached to the lower end oi the shell is electrode I2 in sparking relation with an electrode l3 mounted on the inner end of a conduct-' ing rod ll, the outer end ii of which may be connected with any suitable source of current. Shell i is formed with an internal shoulder i6 upon which there is mounted an insulating ring H which may be constructed of mica washers or equivalent material. The inner end 01' rod it rests upon the ring IT. The rod I4 is coated with a firmly adhering non-conducting coating l8, preferably of enamel of high electric resistance. Enamels of considerable resistance have been developed to insulate conductors, but most of these enamels are not suitable for as high tension as must be met in a spark plug. The addition of calcium borate to enamels otherwise suitable for insulating use renders the enamel more resistant, but it will be understood that in its broader aspect this invention contemplates the use of a sufllciently resistant enamel, however formed, and in this connection the term enamel is employed to cover any insulating coating which is applied to the rod and intimately adherent thereto so as to form the equivalent oi enamel in the construction shown.

Between the lower end of rod II and shell Hi there is compacted powder l9 which may be powdered soapstone or the like. Preferably this powder is of a character to be compacted sufllciently to form a rigid gas-tight body and means for holding rod l4 securely in position within shell Ill. Means is provided at the upper end of the shell to protect body l9 from moisture or the like. In the form shown this protection takes the form of an inturned flange 20.

1936, Serial No. 77,156

In the form shown in Fig. 3 the parts are the same as described in connection with Fig.2 and are numbered the same, with the additional feature that, in the form shown in Fig. 3, a groove is provided in rod H in register with flange 20, and this groove is filled with an annular body 2i of insulating material. This insulating material may be either a separate body as shown in Fig. 3 or where more convenient may be integral with the insulating coating i8. It is obvious that if the insulation is insuiiicient at any point. it will be where the flange 20 approaches closely to rod l4, and consequently extra insulation may be provided as shown in addition to coating l8, if desired, or the coating may be made thicker at this point where necessary; but my preferred form contemplates employing a coating l8 0! sufficient resistance to render it unnecessary to provide additional insulation within flange 20.

The sizes and proportions of parts may, of course, be varied to suit requirements and changes may be made within the scope of the appended claims. The most important single feature of this invention isthe provision of the electrode mounted in a conducting rod, the rod being provided with an insulating coating formed thereon and intimately adherent thereto like enamel, the rod being secured in position within the spark plug shell by frictional engagement with compacted powder or the like.

What I claim is:

1. A spark plug comprising a shell, a central conducting rod, an insulating coating formed on the rod and intimately adherent thereto and compacted powder between the shell and rod forming a gas-tight body and securing the rod in position within the shell. I

2. A spark plug in accordance with claim 1 and having a shell provided with an internal shoulder, an insulating ring mounted upon the shell and the inner end of the rod resting upon said ring.

3. A spark plug in accordance with claim 1 and having the outer end of the body 01' compacted powder protected by an inturned flange of the shell.

4. A spark plug in accordance with claim 1 and having the outer end of the body of compacted powder protected by an inturned flange on the outer end of the shell and having the insulating material around the rod thickened in an annulus within said flange. 

